1. Field of the Invention
The present invention relates to a process unit and an image forming apparatus.
2. Description of the Related Art
In an image forming apparatus of an electrophotographic type, such as a copier, a printer, a facsimile machine, a multifunction peripheral having the respective functions thereof, or the like, a developing device is provided for visualizing a latent image formed on a photosensitive member. Generally speaking, the developing device has a developing roller as a developer carrying member for carrying a toner that is a developer, a supply roller that supplies the toner to the developing roller, a control blade controlling the thickness of the toner on the developing roller into a uniform thickness, and so forth.
Basic operations of the developing device are as follows. First, the toner contained inside the developing device is electrified by friction caused as a result of the supply roller and the developing roller being rubbed together at a nip therebetween, and the toner adheres to the surface of the developing roller by the image force of the electric charge generated by the electrification. Next, when the toner carried by the developing roller reaches a control nip at which the developing roller and the control blade come into contact together, the thickness of the toner is controlled by the control blade to be a uniform thickness, and electric charge is given to the toner. Then, at a developing area between the photosensitive member and the developing roller, the toner on the developing roller is transferred, by a developing electric field, to a latent image formed on the photosensitive member, and the latent image is thus visualized into a toner image. Thus, a desired image is obtained as a result of transfer of the toner being carried out satisfactorily from the supply roller to the developing roller, and from the developing roller to the photosensitive member. Further, for the purpose of stably obtaining a satisfactory image, it is necessary to stabilize the relative position of the developing roller with respect to the photosensitive member.
For example, in an image forming apparatus disclosed in Japanese Laid-Open Patent Application No. 5-66662 (Patent Reference No. 1), a developing device that is rotatably supported has force applied thereto toward a photosensitive member, thus a developing roller is made to come into contact with the photosensitive member via a spacer, and the space between the photosensitive member and the developing roller is made to be constant.
Further, in the image forming apparatus of Patent Reference No. 1, a first gear provided to the developing roller and a second gear provided to the photosensitive member are made to engage together for the purpose of transferring driving force of a motor provided in an apparatus body to the photosensitive member and the developing roller.
However, in the case where the driving force is transferred between the developing device that is rotatably supported and the photosensitive member that is fixed in its position, the developing device may be moved in such a direction that it is rotated because of driving force generated between the gears, and thus, the relative position between the photosensitive member and the developing device may be changed.